This invention relates to a method for preparing catalysts useful in the manufacture of maleic anhydride by the oxidation of aliphatic hydrocarbons, and more particularly it is directed to catalysts suitable for producing maleic anhydride from saturated hydrocarbons in higher yields than heretofore possible.
Maleic anhydride is of significant commercial interest throughout the world. It is used alone or in combination with other acids in the manufacture of alkyd and polyester resins. It is also a versatile intermediate for chemical synthesis. Significant quantities of maleic anhydride are produced each year to satisfy these needs.
The prior art discloses a number of catalysts useful for the conversion of organic feedstocks to maleic anhydride. As an example, U.S. Pat. No. 3,293,268 teaches a process of oxidizing saturated aliphatic hydrocarbons to maleic anhydride under controlled temperature conditions in the presence of a phosphorus-vanadium-oxygen catalyst. U.S. Pat. No. 3,864,280 discloses a phosphorus-vanadium-oxygen catalyst prepared by a method employing an organic solvent to provide a catalyst having a surface area between about 7 and about 50 m.sup.2 /g. U.S. Pat. No. 3,915,892 relates to the preparation of a phosphorus-vanadium-oxygen catalyst using a carefully controlled sequence of steps to heat the precursor to prepare the catalyst. Numerous references are in the prior art relating to phosphorus-vanadium-oxygen catalysts containing a small amount of a promoting element to enhance the yield of maleic anhydride.
Although the prior art catalysts provide acceptable yields of maleic anhydride, it has now been found that the yield of maleic anhydride using a phosphorus-vanadium-oxygen catalyst is significantly improved by controlling the pore size distribution in the finished catalyst. The improved yields of maleic anhydride that are achieved using the catalyst of the present invention wherein the pore size distribution is controlled are far superior to the prior art catalysts.